The invention relates generally to a starting apparatus for cranking an internal combustion engine and more specifically to a pinion gear assembly for momentarily engaging an engine flywheel and transferring power from a starting motor to the internal combustion engine.
The concept and embodiments of automatically engaging and disengaging starting mechanisms for internal combustion engines are well known. A conventional menchanism comprises a plurality of teeth in the flywheel of an internal combustion engine or a ring gear secured to the crank shaft of such engine, juxtaposed a spring-biased pinion gear coupled to the output shaft of a starting motor through a helical spline. When the starting motor is activating and begins to rotate, the inertia of the pinion gear resists rotation and the helical spline causes the pinion to translate axially along the starting motor shaft and into engagement with the gear teeth on the engine crank shaft. The engine is thus cranked until the engine speed surpasses the speed at which the starting motor drives it, whereupon the spring biasing force and helical spline disengage the pinion gear from the engine gear.
Numerous modifications and improvements have been made to this basic mechanism. A particular difficulty of modifying this mechanism is the dimensional constraint placed on its size by associated components. Commonly, the starter mechanism will be positioned within a housing or adjacent engine components which closely limit its size. Therefore, unless redesign of the entire starting motor assembly and perhaps even engine components is permitted, refinements to the starter mechanism must be made within dimensional limits established by these associated components. The development of a new component or production technique thus leads to the additional consideration of adapting such an improvement to the presently utilized components.
A conventional starting motor pinion gear assembly includes an outer metal cup or shell which secures, in operating relationship, a spline follower, a resilient washer which functions as a friction clutch and the pinion gear itself. The cup is secured to the pinion gear and these components are frictionally driven through the clutch washer by the spline follower in the manner previously explained.
Prior art pinion gears are commonly hobbed or drop forged and may easily be attached to the drawn cup by conventional means such as welding or brazing as is taught by U.S. Pat. No. 3,071,013. The recently developed capability of forming the pinion gears of powdered metal and then sintering them, produces an improved pinion gear but creates difficulties with regard to the mode of attachment of the pinion to the drawn cup. Conventional welding and brazing techniques while ultimately capable of performing such a bonding operation, reliably do so only under carefully controlled conditions and the rejection rate of completed assemblies and the difficulties inherent in such a bonding process offset the advantages of a powdered metal pinion gear.
One attempt at solving the problem of securing the pinion to the drawn cup involves punching the radial face of the cup with a die conforming to the outline of the pinion gear, passing the pinion through the punched opening in the cup and retaining it within the cup by means of a radially extending ridge adjacent one end of the pinion. If the diameter of the drawn cup is sufficiently large to permit the pinion gear to be passed within its inside diameter, this approach is viable. However, as the number of teeth on the pinion gear and its outside diameter increase, this mounting approach becomes unusable inasmuch as either there is insufficient material on the radial face of the cup to either punch or insure proper retention of the pinion or the outside diameter of the pinion exceeds the inside diameter of the cup. In the largest pinions, typically having 11 teeth, the outer diameter of the pinion is nearly identical to the outer diameter of the drawn cup and the punched radial face mounting scheme is patently unusable. Due to the dimensional constraints of the associated components noted previously, enlarging the diameter of the drawn cup to accept and secure the pinions is, likewise, an approach which is not viable.